Autonomous Power System with Variable Sources and Loads and Associated Methods

ABSTRACT

A number of load units are connected to receive power from a number of power supply units. A potential load bus is connected to have a voltage level representative of both a total potential power requirement of the number of load units and a total potential power supply capability of the number of power supply units. A first control circuit enables operation of the number of load units when the voltage level on the potential load bus indicates that a sufficient supply of power is available. An actual load bus is connected to have a voltage level representative of both an actual total power consumption of the number of load units and an actual total power supply available from of the number of power supply units. A second control circuit signals an impending loss of sufficient power supply based on the monitored voltage level on the actual load bus.

BACKGROUND

Units of computing systems and other electronic products are oftenmounted in rack enclosures to achieve a dense vertical stacking. Theracks are often standardized at 19 inches or 23 inches of front panelwidth, have standard mounting hole positions, and provide areas forconnecting interface cables and power to the units in the rack. Theunits may be interconnected to work together or may be independent andonly in the same rack because of available space and power connections.

Input power for units in a rack may be standard AC (alternating current)power but may also be from one or more power converting units thatprovide power for some or all of the units in the rack, i.e., loadunits. The power converting units often provide functions such asredundant inputs and provide a DC (direct current) output. Providingisolation from primary input power, input redundancy, and powerconversion to a regulated DC voltage in a separate power unit allows theother load units in the rack to be smaller and more efficient since theydo not need their own power supplies to perform those functions. When apower converting unit is incorporated in a rack or otherwise used toprovide power for a group of load units, there is a need forcommunication between the load units and the power converting unit toensure reliable operation of the load units. It is within this contextthat the present invention arises.

SUMMARY

In one embodiment, a power system is disclosed. The power systemincludes a number of power supply units, and a number of load unitsconnected to receive power from the number of power supply units. Thepower system includes a potential load bus connected to have a voltagelevel representative of both a total potential power requirement of thenumber of load units and a total potential power supply capability ofthe number of power supply units. The power system also includes a firstcontrol circuit connected to the potential load bus and defined tomonitor the voltage level on the potential load bus and enable operationof one or more of the number of load units when the voltage level on thepotential load bus indicates that a sufficient supply of power isavailable from the number of power supply units for operation of the oneor more of the number of load units. The power system also includes anactual load bus connected to have a voltage level representative of bothan actual total power consumption of the number of load units and anactual total power supply available from of the number of power supplyunits. The power system further includes a second control circuitconnected to the actual load bus and defined to monitor the voltagelevel on the actual load bus and based on the monitored voltage level onthe actual load bus signal an impending loss of the sufficient supply ofpower from the number of power supply units for operation of the one ormore of the number of load units.

In one embodiment, a method is disclosed for operating a power system.The method includes applying a separate electrical current to apotential load bus for each of a number of operating power supply units.Each separate electrical current applied to the potential load bus isscaled in magnitude relative to a power supply capability of a givenpower supply unit to which the separate electrical current corresponds.The method also includes connecting a separate resistor between thepotential load bus and a reference ground potential for each of a numberof load units that are to receive power from the number of operatingpower supply units. Each separate resistor connected to the potentialload bus has an electrical resistance scaled in magnitude relative to apower consumption of a given load unit to which the separate resistorcorresponds. The method also includes comparing a voltage level on thepotential load bus to a threshold voltage level to determine whether ornot a sufficient supply of power is available from the number ofoperating power supply units for operation of the number of load units.

In one embodiment, a method is disclosed for configuring a power system.The method includes installing a number of power supply units andinstalling a number of load units. The method also includes connectingthe number of load units to receive power from the number of powersupply units. The method also includes connecting a separate firstelectric current source to supply electrical current to a potential loadbus for each of the number of power supply units. Each first electricalcurrent source is defined to supply an amount of electrical currentbased on a power output rating of a given one of the number of powersupply units to which it corresponds. The method also includesconnecting a separate first resistor to the potential load bus for eachof the number of load units. Each first resistor is defined to providean amount of electrical resistance based on a power consumption of agiven one of the number of load units to which it corresponds. Themethod further includes connecting a separate first voltage comparatordevice to the potential load bus for each of the number of load units.Each first voltage comparator device has a first input connected to thepotential load bus and a second input connected to a reference voltagesupply to be set at a threshold voltage level and an output connected toa power control circuit of a given one of the number of load units towhich it corresponds.

Other aspects of the invention will become more apparent from thefollowing detailed description, taken in conjunction with theaccompanying drawings, illustrating by way of example the presentinvention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a computing system that includes a number of power supplyunits and a number of load units, i.e., computing units or datamanagement/transmission devices, in accordance with one embodiment ofthe present invention.

FIG. 2A shows a power system, in accordance with one embodiment of thepresent invention.

FIG. 2B shows a power system that is a variation of the power system ofFIG. 2A, in accordance with one embodiment of the present invention.

FIG. 2C shows the power systems in which a third control circuit isprovided to control release of output power from the power supply unitsto the power bus that services the load units, in accordance with oneembodiment of the present invention.

FIG. 3 shows a power system as an example implementation of the powersystem, in accordance with one embodiment of the present invention.

FIG. 4 shows an implementation of the load unit of the example of FIG. 3in power system of FIG. 2B, in accordance with one embodiment of thepresent invention.

FIG. 5A shows a flowchart of a method for operating a power system, inaccordance with one embodiment of the present invention.

FIG. 5B shows a flowchart of a method for operating a power system, inaccordance with one embodiment of the present invention.

FIG. 6A shows a flowchart of a method for configuring a power system, inaccordance with one embodiment of the present invention.

FIG. 6B shows a flowchart of a method for configuring a power system, inaccordance with one embodiment of the present invention.

DETAILED DESCRIPTION

It should be appreciated that the present invention can be implementedin numerous ways, including as a process, an apparatus, a system, adevice, or a method. Several exemplary embodiments of the invention willnow be described in detail with reference to the accompanying drawings.In the following description, numerous specific details are set forth inorder to provide a thorough understanding of the present invention. Itwill be apparent, however, to one skilled in the art that the presentinvention may be practiced without some or all of these specificdetails. In other instances, well known process operations have not beendescribed in detail in order not to unnecessarily obscure the presentinvention.

FIG. 1 shows a computing system 101 that includes a number of powersupply units 105 and a number of load units 103, i.e., computing unitsor data management/transmission devices, in accordance with oneembodiment of the present invention. It should be understood that theload units 103 can be any type of computing device or system componentthat receives power from the power supply units 105. For example, agiven load unit 103 may be a computing server module, a processormodule, a storage server module, a shared storage module, a networkswitch, or any other type of computing/data management device. Also, agiven power supply unit 105 can be any type of power supply unit definedto supply electrical power to a power bus that services the load units103 within the computing system 101. In one embodiment, the power supplyunits 105 receive alternating current electrical power from anelectrical service supply line, convert the received alternating currentelectrical power into direct current power of specified voltage andamperage, and supply the direct current power to the power bus of thecomputing system 101.

In various embodiments of the computing system 101, the power supplyunits 105 and the load units 103 may or may not have a means ofcommunicating with each other. For example, in one embodiment, thecomputing system 101 is a “dumb” system in which its power supply units105 automatically turn on and attempt to provide power to its load units103, without knowing what the total required load power is for theinstalled/operating load units 103. In this embodiment, if the requiredload power of the operating load units 103 exceeds the power supplycapacity of the power supply units 105, the power supply units 105 maysuffer an overload and be forced to shut off the power supply to theload units 103. Also, in the “dumb” system embodiment, when operation isachieved, the load units 103 will not be able to receive informationabout the status of the power supply units 105 and may suffer a suddenand unexpected loss of power in the event of power supply unit 105failure. It should be appreciated that if the supply of power to a loadunit 103 is shut off, the load unit 103 may suffer unrecoverable dataloss and corruption of essential data in memory. Also, in the “dumb”system embodiment, adding a load unit 103 to the computing system 101that is already in operation may result in an overload of the powersupply units 105 and corresponding unexpected loss of power to all loadunits 103. The “dumb” system may not be desirable for computingequipment due to the lack of power failure warning. Most computingequipment requires some amount of warning prior to loss of power toprevent data corruption and/or hardware damage.

In another embodiment, the computing system 101 is a “normal” system inwhich the power supply units 105 are defined to provide status signalsto the load units 103, such as a high temperature warning signal orinput power loss warning signal, among others, to allow the load units103 to prepare for a loss of power event. However, like the “dumb”system, the “normal” system is defined such that its power supply units105 automatically turn on and attempt to provide power to its load units103, without knowing what the total required load power is for theinstalled/operating load units 103. Thus, the “normal” system may alsosuffer from initial overloads or power failure when more load units 103are added. The “normal” system is useful for fixed computing systemconfigurations in which new load units 103 will not be added. In a fixedcomputing system configuration, the power supply units 105 are designedto have more power output capacity that the total power required by theload units 103. Also, in the “normal” system, the power supply units 105warn the load units 103 of an impending power failure.

In another embodiment, the computing system 101 is a “smart” system inwhich a separate power controller module 107 is connected to manage thesupply of power from the power supply units 105 to the load units 103.In one embodiment, the controller becomes active from standby or fromthe supply of main output power and directs the turn on of the loadunits 103 in the computing system 101. The power controller module 107communicates with the power supply units 105 to know their output powercapability. The power controller module 107 also communicates with theload units 103 to know how much power each load unit 103 requires. Thepower controller module 107 can then determine which of the load units103 may be allowed to operate and prohibit operation of any load unit103 that would cause an overload condition in which the total powerconsumption of the operating load units 103 exceeds the total powersupply capability of the power supply units 105.

Also, the power controller module 107 operates to ensure that operationof any load unit 103 that is added to the computing system 101 iscontingent upon a comparison of the newly added load unit's 103 powerneeds to the available power capacity of the power supply units 105.Similar to the “normal” system, the power supply units 105 of the“smart” system are defined to provide warning signals to the load units103 of impending power failure, since the delay of transmitting warningsignals through the power controller module 107 would not allow the loadunits 103 enough time to prepare for the imminent loss of power event.

The “smart” system is useful in highly configurable computing systems.The “smart” system may provide for variability in both the output powercapability and the number of power supply units 105 that can beinstalled. The “smart” system can also be used with a wide selection ofload units 103, including compute nodes, data storage units, and/orunits to provide connectivity for transferring data in and out of thecomputing system, among others. An example of a “smart” system in theChassis Management Module in the Sun Blade 6000, which is an intelligentpower controller module 107 defined to gather data from all systemcomponents and manage the power supply units 105 and load units 103 suchthat there is minimal chance of an overload causing the power supplyunits 105 to fail.

It should be appreciated that the separate power control module 107required of the “smart” system adds expense to the overall computingsystem. To avoid the added expense and complexity of the power controlmodule 107, it is desirable to have a power system that provides theinitial startup and overload protections of the “smart” system with thesimple and less expensive configuration of the “normal” system. It is tothis end that the present invention is provided. Specifically, thepresent invention provides a power system and associated methods ofoperation and configuration in which necessary information is providedbetween the power supply units 105 and load units 103 to achieve theinitial startup and overload protections afforded by the “smart” systemwithout the expense and complexity of the separate power control module107 that is required in the “smart” system.

FIG. 2A shows a power system 200, in accordance with one embodiment ofthe present invention. The power system 200 includes a number of powersupply units 205. The power supply system 200 also includes a number ofload units 203 connected to receive power from the number of powersupply units 205. The power system 200 also includes a potential loadbus 207 connected to have a voltage level representative of both a totalpotential power requirement of the number of load units 203 and a totalpotential power supply capability of the number of power supply units205. The power system 200 further includes a first control circuit 209connected to the potential load bus 207. The first control circuit 209is also referred to as the Potential Control Circuit 209. The firstcontrol circuit 209 is defined to monitor the voltage level on thepotential load bus 207 and enable operation of one or more of the numberof load units 203 when the voltage level on the potential load bus 207indicates that a sufficient supply of power is available from the numberof power supply units 205 for operation of the one or more of the numberof load units 203.

The power system 200 also includes an actual load bus 211 connected tohave a voltage level representative of both an actual total powerconsumption of the number of load units 203 and an actual total powersupply available from of the number of power supply units 205. The powersystem 200 further includes a second control circuit 213 connected tothe actual load bus 211. The second control circuit 213 is also referredto as the Actual Control Circuit 213. The second control circuit 213 isdefined to monitor the voltage level on the actual load bus 211, andbased on the monitored voltage level on the actual load bus 211 signalan impending loss of the sufficient supply of power from the number ofpower supply units 205 for operation of the one or more of the number ofload units 203.

The first control circuit 209 is defined to compare the voltage level ofthe potential load bus 207 to a threshold voltage level to determinewhether or not each of the number of load units 203 is to be enabled foroperation. In one embodiment, the first control circuit 209 is definedto enable the number of load units 203 for operation on an individualload unit 203 basis when the voltage level of the potential load bus 207is greater than the threshold voltage level. In one embodiment, thefirst control circuit 209 includes separate voltage comparator devices215 respectively connected to the number of load units 203. Each of theseparate voltage comparator devices 215 has a first input 217 connectedto the potential load bus 207 and a second input 219 connected to areference voltage supply 218 to be set at the threshold voltage level,and an output 221 connected to a power control circuit input 222 of theload unit 203 to which the voltage comparator device 215 is connected.

The second control circuit 213 is defined to compare the voltage levelof the actual load bus 211 to a threshold voltage level to determinewhether or not an actual total supply of power from the number of powersupply units 205 is sufficient to support continued operation of thenumber of load units 203 that are in an operating state. In oneembodiment, the second control circuit 213 is defined to transmit apower fault warning signal when the voltage level of the actual load bus211 is less than the threshold voltage level. In one embodiment, thepower fault warning signal is transmitted instantaneously andcontinuously from the second control circuit 213 to each of the numberof load units 203 when the voltage level of the actual load bus 211 isless than the threshold voltage level. In one embodiment, the secondcontrol circuit 213 includes separate voltage comparator devices 223respectively connected to the number of load units 203. Each of theseparate voltage comparator devices 223 has an output 225 connected to apower control circuit input 226 of the load unit 203 to which thevoltage comparator device 223 is connected. Each of the separate voltagecomparator devices 223 has a first input 227 connected to the actualload bus 211, and a second input 229 connected to a reference voltagesupply 231 to be set at the threshold voltage level.

The power system 200 also includes a first number of resistors 233connected between the potential load bus 207 and a reference groundpotential 235. The first number of resistors 233 respectively correspondto the number of load units 203. Each of the first number of resistors233 has an amount of electrical resistance based on a power consumptionof the load unit 203 to which it corresponds. In one embodiment, thefirst number of resistors 233 includes at least one resistor 233X thatdoes not correspond to one of the number of load units 203. The at leastone resistor 233X has an amount of electrical resistance based on aprescribed amount of power supply margin.

The power system 200 also includes a first number of current sources 237connected to supply electrical current to the potential load bus 207.The first number of current sources 237 respectively correspond to thenumber of power supply units 205. Each of the first number of currentsources 237 is defined to supply an amount of electrical current basedon a power output rating of the power supply unit 205 to which itcorresponds.

The power system 200 also includes a second number of resistors 239connected between the actual load bus 211 and the reference groundpotential 235 through a corresponding controllable connection device 241defined to connect its resistor 239 to the reference ground potential235 when its corresponding load unit 203 is an operating state. In oneembodiment, the controllable connection device 241 is defined as atransistor, such as an NMOS or PMOS transistor. However, it should beunderstood that in other embodiments, the controllable connection device241 can be defined as essentially any type of electrical device thatperforms an electrical switching function in response to a controlsignal. The second number of resistors 239 respectively correspond tothe number of load units 203. Each of the second number of resistors 239has an amount of electrical resistance based on power consumption of theload unit 203 to which it corresponds, such that for a given one of thenumber of load units 203 the amount of electrical resistance of each ofthe corresponding one of the second number of resistors 239 and thecorresponding one of the first number of resistors 233 is substantiallyequal.

The power system 200 also includes a second number of current sources243 connected to supply electrical current to the actual load bus 211.The second number of current sources 243 respectively correspond to thenumber of power supply units 205. Each of the second number of currentsources 243 is defined to supply an amount of electrical current basedon a power output rating of the power supply unit 205 to which itcorresponds, such that for a given one of the number of power supplyunits 205 the amount of electrical current to be supplied by each of thecorresponding one of the second number of current sources 243 and thecorresponding one of the first number current sources 237 issubstantially equal. In one embodiment, each of the number of powersupply units 205 is defined to control activation of its correspondingone of the first number of current sources 237 and its corresponding oneof the second number of current sources 243.

FIG. 2B shows a power system 200A that is a variation of the powersystem 200 of FIG. 2A, in accordance with one embodiment of the presentinvention. The power system 200A includes each feature previouslyidentified with regard to the power system 200 of FIG. 2A. The powersystem 200A differs from the power system 200 in that each of the firstnumber of resistors 233 is connected to the reference ground potential235 by way of a corresponding controllable connection device 245. Thecontrollable connection devices 245 respectively connected to the firstnumber of resistors 233 to provide individual control of an electricalconnection between the first number of resistors 233 and the referenceground potential 235, such that a given one of the first number ofresistors 233 is connected to the reference ground potential 235 whenthe load unit 203 corresponding to the given one of the first number ofresistors 233 issues a request to receive power.

FIG. 2C shows the power system 200 in which a third control circuit 247is provided to control release of output power from the power supplyunits 205 to the power bus that services the load units 203, inaccordance with one embodiment of the present invention.

The third control circuit 247 is also referred to as a power outputcontrol circuit 247. It should be understood that the potential controlcircuit 209 and actual control circuit 213 as shown in FIG. 2C includesthe components are corresponding connections as previously describedwith regard to FIG. 2A. Also, it should be understood that the thirdcontrol circuit 247 can be implemented with the power system 200A ofFIG. 2B in an equivalent manner as shown in FIG. 2C with regard to thepower system 200.

In one embodiment, the third control circuit 247 is defined to disableoutput of power from the number of power supply units 205 to the numberof load units 203 until an actual total available supply of power fromthe number of power supply units 205 is sufficient to support operationof the number of load units 203 that are requesting power. In thisembodiment, the third control circuit 247 is defined to enable output ofpower from the number of power supply units 205 to the number of loadunits 203 when the actual total available supply of power from thenumber of power supply units 205 is sufficient to support operation ofthe number of load units 203.

In one embodiment, the third control circuit 247 is defined to comparethe voltage level of the potential load bus 207 to a threshold voltagelevel to determine whether or not output of power from the number ofpower supply units 205 is to be enabled or disabled. For instance, inone embodiment, the third control circuit 247 is defined to enableoutput of power from the number of power supply units 205 to the numberof load units 203 when the voltage level of the potential load bus 207is greater than the threshold voltage level, and disable output of powerfrom the number of power supply units 205 to the number of load units203 when the voltage level of the potential load bus 207 is less thanthe threshold voltage level.

In the example embodiment of FIG. 2C, the third control circuit 247includes separate voltage comparator devices 249 respectively connectedto the number of power supply units 205. Each of the separate voltagecomparator devices 249 has a first input 251 connected to the potentialload bus 207, and a second input 253 connected to a reference voltagesupply 255 to be set at the threshold voltage level. Each of theseparate voltage comparator devices 249 has an output 257 connected to apower output control of the power supply unit 205 to which the voltagecomparator device 249 is connected.

Unlike the above-mentioned “normal” power system, the power system200/200A of the present invention provides the potential load bus 207,whose voltage level can be monitored in real-time to provide poweroverload warning/protection during initial startup and during operationwhen anew load unit 203 is added. Also, unlike the above-mentioned“normal” power system, the power system 200/200A of the presentinvention provides the actual load bus 211, whose voltage level can bemonitored in real-time during operation to provide power losswarning/protection in the event that one or more power supply units 205go offline during operation. In addition, it should be appreciated thatthe power system 200/200A of the present invention does not require theseparate power control module 107 of the above-mentioned “smart” powersystem and its associated expense and complexity. In other words, thepower system 200/200A of the present invention functions autonomously ina manner that provides power overload warning/protection, but withoutthe need for a separate power control module 107.

In one embodiment, the power supply units 205 are inhibited fromsupplying power to the main power bus until the total power capacityavailable equals or exceeds the total power needs of the load units 203.In one embodiment, new load units 203 that are added to an operatingcomputing system will have their power requirements compared to theavailable power capacity to determine if they can be activated. Itshould be appreciated that in the power system 200/200A, impending powerfailure warnings from the power supply units 205 are incorporated intothe two wire interface formed by the actual load bus 211 and potentialload bus 207, such that transmission of additional signals between thepower supply units 205 and load units 203 is not required.

The potential load bus 207 and actual load bus 211 provide a two wireinterface that connects all power supply units 205 to all load units203. In one embodiment, the two wire interface uses low voltage signals,e.g., less than 5 Volts, that are isolated from the primary power bus towhich the power supply units 205 are connected to supply power. Morespecifically, a first low voltage signal is provided on the potentialload bus 207, and a second low voltage signal is provided on the actualload bus 211. The potential load bus 207 is pulled toward a highervoltage level by the current sources 237. The potential load bus 207 ispulled toward a lower voltage level by the resistors 233. The actualload bus 211 is pulled toward a higher voltage level by the currentsources 243. The actual load bus 211 is pulled toward a lower voltagelevel by the resistors 239.

All devices connected by the two bus wires, i.e., by the potential loadbus 207 and by the actual load bus 211, have voltage threshold detectorsto determine if each voltage on the potential load bus 207 and actualload bus 211 is above or below a certain reference voltage (or thresholdvoltage). Specifically, the voltage comparator devices 215 are connectedto determine if the voltage on the potential load bus 207 is above orbelow the threshold voltage set by the reference voltage supply 218.And, the voltage comparator devices 223 are connected to determine ifthe voltage on the actual load bus 211 is above or below the thresholdvoltage set by the reference voltage supply 231. In one embodiment, thereference voltage supplies 218 and 231 are defined separate from eachother. In another embodiment, the reference voltage supplies 218 and 231correspond to a single, i.e., same, reference voltage supply.

The potential load bus 207 is used by the power supply units 205 whenthe computing system is starting from an off condition without inputpower for the power supply units 205 or when the computing system isrestarting after a fault condition. There can be multiple power supplyunits 205 operating in parallel for a large power load and the powersupply units 205 may or may not have equal output power capabilities.Each load unit 203 has its corresponding resistor 233 connected to thepotential load bus 207. The resistor 233 corresponding to a given loadunit 203 has an electrical resistance to the reference ground potential235, e.g., system ground, that corresponds to the amount of electricalpower that the given load unit 203 will need. As each power supply unit205 receives input power and becomes ready to deliver power to the mainpower bus and ultimately to the load units 203, the power supply unit205 directs connection of its corresponding current source 237 to thepotential load bus 207. The current source 237 corresponding to a givenpower supply unit 205 provides an amount of electrical current to thepotential load bus 207 based on the power output capacity of the givenpower supply unit 205. Each current source 237 increases the voltage onthe potential load bus 207.

In one embodiment, the power supply units 205 do not begin deliveringpower to the main power bus unless the voltage on the potential load bus207 has reached its prescribed threshold voltage level. The prescribedthreshold voltage level of the potential load bus 207 that is requiredfor the power supply units 205 to start delivering power to the mainpower bus is set such that the power supply units 205 will havesufficient total power output capacity to power all of the load units203 that are connected in the computing system.

After the computing system is in operation, the potential load bus 207functions to provide areal-time test of the ability of the total poweroutput capacity of the power supply units 205 to support addition of anew load unit 203 in combination with the already operational load units203. When anew load unit 203 is to be added to the computing system, aresistor 233 associated with the new load unit 203 is connected to thepotential load bus 207. The resistor 233 associated with the new loadunit 203 has an electrical resistance based on the new load unit's powerrequirement.

The voltage comparator device 215 corresponding to the new load unit 203operates to determine if the voltage on the potential load bus 207,after connection of the new load unit's resistor 233, is still above thethreshold voltage level indicative of having a sufficient supply ofpower from the power supply units 205. If the voltage on the potentialload bus 207 remains above the threshold voltage level after connectionof the new load unit's resistor 233, the new load unit 203 is allowed toturn on and receive power from the main power bus. However, if thevoltage on the potential load bus 207 falls below the threshold voltagelevel after connection of the new load unit's resistor 233, the new loadunit 203 is not allowed to turn on and receive power from the main powerbus, thereby protecting the computing system from a potential poweroverload condition.

The current sources 243 that are connected to the actual load bus 211serve to pull up the voltage on the actual load bus 211. The currentsources 243 that are connected to the actual load bus 211 are similar toor identical to the current sources 237 that are connected to thepotential load bus 207. As with the current sources 237, the currentsources 243 can be defined within its corresponding power supply unit205 or defined outside its corresponding power supply unit 205. Theresistors 239 that are connected to the actual load bus 211 serve topull down the voltage on the actual load bus 211. The resistors 239 thatare connected to the actual load bus 211 are similar to or identical tothe resistors 233 that are connected to the potential load bus 207.However, unlike the resistors 233 that are connected to the potentialload bus 207, each resistor 239 that is connected to the actual load bus211 is only connected to the reference ground potential 235, by way ofits controllable connection device 241, when the load unit 203associated with the resistor 239 is activated and receiving power fromthe main power bus of the computing system.

When a given load unit 203 has been allowed to turn on because thevoltage level on the potential load bus 207 is greater than the requiredthreshold voltage level, the controllable connection device 241 isoperated to connect the resistor 239 corresponding to given load unit203 to the reference ground potential 235, thereby lowering the voltagelevel on the actual load bus 211 to reflect the power consumption of thegiven load unit 203. In one embodiment, the controllable connectiondevice 241 is defined as an electrical switching device, such as aMOSFET, connected between its corresponding resistor 239 and thereference ground potential 235. It should be appreciated that thevoltage level on the actual load bus 211 represents a real-timecomparison between the total power output capacity of the power supplyunits 205 and the total power requirements of the operating, i.e.,active, load units 203.

With the computing system in operation and a number of load units 203operating, the actual load bus 211 provides the function of warning theload units 203 of a power supply unit 205 shut down (deactivation orfailure), by way a drop in voltage on the actual load bus 211 when thecurrent source 243 corresponding to the shut down power supply unit 205is immediately turned off in conjunction with the shut down of the powersupply unit 205. For example, if a given power supply unit 205 needs toshut down for some reason, e.g., exceeding temperature limit, the givenpower supply unit 205 can turn off its corresponding current source 243a short period of time before the given power supply unit 205 stopssupplying power to the main power bus of the computing system. By way ofexample, the current source 243 can be turned off a few tens ofmilliseconds before its corresponding power supply unit 205 stopssupplying power to the main power bus. Then, if the loss of the givenpower supply unit 205 will reduce the total available power on the mainpower bus to a level that the remaining operational power supply units205 may overload or fail, the shut off of the current source 243associated with the given power supply unit 205 will cause the voltagelevel on the actual load bus 211 to fall below the threshold voltagelevel that indicates sufficient power availability, thereby providing awarning to the load units 203 to prepare for a possible imminent loss ofpower event.

In addition to overheating and/or device failure, another cause forpower loss is a failure of the input power source to one or more of thepower supply units 205. It should be appreciated, however, that theloss-of-power warning provided through monitoring of the voltage levelon the actual load bus 211 is not affected by the root cause of thepower loss. Each power supply unit 205 can have some amount of energystorage capacity to provide residual power output to the main powersource in the even that the power supply unit 205 shuts down. In oneembodiment, the power supply unit 205 can provide up to 10 millisecondsor more of residual power output to the main power bus after shut downof the power supply unit 205. In one embodiment, once a given powersupply unit 205 is turned on, the given power supply unit 205 may ignorethe voltage levels present on the potential load bus 207 and actual loadbus 211, and only turn off for an overload or other fault condition.Also, in one embodiment, when a fault condition causes a given powersupply unit 205 to turn off, the given power supply unit 205 may remaininactive for a set delay time and then reactivate its current sources237, 243 to begin a restart sequence.

FIG. 3 shows a power system 300 as an example implementation of thepower system 200, in accordance with one embodiment of the presentinvention. The power system 300 includes three power supply units 205-0,205-1, 205-2, and three load units 203-0, 203-1, 203-2. It should beunderstood that the three power supply units 205-0, 205-1, 205-2 and thethree load units 203-0, 203-1, 203-2 in the power system 300 areprovided by way of example. In other embodiments, the power system200/200A can include any number of power supply units 205 and any numberof load units 203. In the example power system 300, the power supplyunits 205-0, 205-1, 205-2 include current sources 237-0, 237-1, 237-2,respectively, connected to the potential load bus 207, and currentsources 243-0, 243-1, 243-2, respectively, connected to the actual loadbus 211. Each of the current sources 237-0, 237-1, 237-2 turns on whenits power supply unit 205-0, 205-1, 205-2 is ready to supply power tothe main power bus. Each of the current sources 243-0, 243-1, 243-2turns on when its power supply unit 205-0, 205-1, 205-2 is activelysupplying power to the main power bus.

Also, in the example power system 300, the power supply units 205-0,205-1, 205-2 include the voltage comparator devices 249-0, 249-1, 249-2,respectively, having a first input connected to the potential load bus207. The voltage comparator devices 249-0, 249-1, 249-2 each have asecond input connected to the reference voltage supplies 255-0, 255-1,255-2, respectively. In the example power system 300, the referencevoltage supplies 255-0, 255-1, 255-2 are each defined to supply areference voltage of about 1 Volt to the second input of its respectiveone of the voltage comparator devices 249-0, 249-1, 249-2.

Each of the voltage comparator devices 249-0, 249-1, 249-2 has arespective output 257-0, 257-1, 257-2 connected to provide acorresponding output enable signal to the power supply unit 205-0,205-1, 205-2 in which the voltage comparator device 249-0, 249-1, 249-2is defined. The output enable signals provided by the voltage comparatordevices 249-0, 249-1, 249-2 direct the corresponding power supply units205-0, 205-1, 205-2 as to when they can release power to the main powerbus. In the example power system 300, the output enable signals providedby the voltage comparator devices 249-0, 249-1, 249-2 will direct thecorresponding power supply units 205-0, 205-1, 205-2 to release power tothe main power bus when the voltage level on the potential load bus 207is greater than the reference voltage of 1 Volt.

In the example power system 300, the load units 203-0, 203-1, 203-2include resistors 233-0, 233-1, 233-2, respectively, connected to thepotential load bus 207 and resistors 239-0, 239-1, 239-2, respectively,controllably connected to the actual load bus to 211. Controllableconnection devices 241-0, 241-1, 241-2 are connected to controlconnection of the resistors 239-0, 239-1, 239-2 to the reference groundpotential, such that the resistors 239-0, 239-1, 239-2 are connected tothe reference ground potential when its corresponding load unit 203-0,203-1, 203-2 is turned on and operating, and such that the resistors239-0, 239-1, 239-2 are not connected to the reference ground potentialwhen its corresponding load unit 203-0, 203-1, 203-2 is not turned onand operating.

Also, in the example power system 300, the load units 203-0, 203-1,203-2 include the voltage comparator devices 215-0, 215-1, 215-2,respectively, having a first input connected to the potential load bus207, and a second input connected to the reference voltage supplies218-0, 218-1, 218-2, respectively. In the example power system 300, thereference voltage supplies 218-0, 218-1, 218-2 are each defined tosupply a reference voltage of about 1 Volt to the second input of itsrespective one of the voltage comparator devices 215-0, 215-1, 215-2.

Each of the voltage comparator devices 215-0, 215-1, 215-2 has arespective output 222-0, 222-1, 222-2 connected to provide acorresponding power on control signal to the load unit 203-0, 203-1,203-2 in which the voltage comparator device 215-0, 215-1, 215-2 isdefined. In the example power system 300, the power on control signalsprovided by the voltage comparator devices 215-0, 215-1, 215-2 willdirect the corresponding load units 203-0, 203-1, 203-2 to turn on whenthe voltage level on the potential load bus 207 is greater than thereference voltage of 1 Volt.

In the example power system 300, the load units 203-0, 203-1, 203-2 alsoinclude the voltage comparator devices 223-0, 223-1, 223-2,respectively, having a first input connected to the actual load bus 211,and a second input connected to the reference voltage supplies 231-0,231-1, 231-2, respectively. In the example power system 300, thereference voltage supplies 231-0, 231-1, 231-2 are each defined tosupply a reference voltage of about 1 Volt to the second input of itsrespective one of the voltage comparator devices 223-0, 223-1, 223-2.

Each of the voltage comparator devices 223-0, 223-1, 223-2 has arespective output 226-0, 226-1, 226-2 connected to provide acorresponding power fault signal to the load unit 203-0, 203-1, 203-2 inwhich the voltage comparator device 223-0, 223-1, 223-2 is defined. Inthe example power system 300, the power fault signals provided by thevoltage comparator devices 223-0, 223-1, 223-2 will provide an imminentloss of power warning to the corresponding load units 203-0, 203-1,203-2 when the voltage level on the actual load bus 211 falls below thereference voltage of 1 Volt, thereby providing the load units 203-0,203-1, 203-2 an amount of time to prepare for power loss on the mainpower bus. As previously mentioned, the power supply units 205-0, 205-1,205-2 have an amount of residual, i.e., capacitive, power outputcapability upon shut down, which provides the amount of time for theload units 203-0, 203-1, 203-2 to prepare for power loss on the mainpower bus.

In the example power system 300, the power supply units 205-0, 205-1,205-2 have power output capacities of 1 kilowatt (kW), 1.2 kW, and 0.5kW, respectively. The current sources 237-0, 237-1, 237-2, 243-0, 243-1,243-2 in the power supply units 205-0, 205-1, 205-2 are scaled toprovide an output current of 1 milliamp (mA) per 1 kilowatt of poweroutput capacity of its corresponding power supply unit 205-0, 205-1,205-2. Thus, the current sources 237-0 and 243-0 each provide an outputcurrent of 1 mA. The current sources 237-1 and 243-1 each provide anoutput current of 1.2 mA. And, the current sources 237-2 and 243-2 eachprovide an output current of 0.5 mA.

The equivalent bus resistance for each load unit 203-0, 203-1, 203-2 isthen set at (1000 Watts×1000 Ohms) divided by the power required foreach load unit 203-0, 203-1, 203-2 in Watts. Therefore, the resistors233-0 and 239-0 each have a resistance of about 4 kiloOhms (K) for theload unit 203-0. The resistors 233-1 and 239-1 each have a resistance ofabout 1 K for the load unit 203-1. And, the resistors 233-2 and 239-2each have a resistance of about 0.5 K for the load unit 203-2. Withthese choices for the current sources 237-0, 237-1, 237-2, 243-0, 243-1,243-2 and resistors 233-0, 233-1, 233-2, 239-0, 239-1, 239-2, thevoltage on each of the potential load bus 207 and actual load bus 211will be above 1 Volt if the total power output capacity of the powersupply units 205-0, 205-1, 205-2 is greater than the total powerrequired by the load units 203-0, 203-1, 203-2, and below 1 Voltotherwise. Therefore, the voltage threshold for the potential load bus207 and the actual load bus 211 buses is set at about 1 Volt.

In the example power system 300, the power supply units 205-0, 205-1,205-2 will be enabled when their total power output capacity exceeds4.25 kW. The 4.25 kW threshold is set by the parallel combination ofresistors 233-0, 233-1, 233-2, and 233X. A current of 4.25 mA or greatermust be present from the power sources to raise the voltage on bus 207to more than 1 Volt. Then, when the power supply units 205-0, 205-1,205-2 are enabled and supplying power to the main power bus, all loadunits 203-0, 203-1, 203-2 will be allowed to turn on because the voltageon the potential load bus 207 will be greater than 1 Volt. As the loadunits 203-0, 203-1, 203-2 turn on, their corresponding resistors 239-0,239-1, 239-2 will be connected between the actual load bus 211 and thereference ground potential by way of the corresponding controllableconnection devices 241-0, 241-1, 241-2. Initially, the voltage on theactual load bus 211 will also be greater than 1 V, as the actual loadbus 211 is initially a duplicate of the potential load bus 207 withregard to its electrical connections.

If an additional load unit is added to the computing system, theadditional load unit will have a corresponding additional load resistor233 connected between the potential load bus 207 and the referenceground potential. Connection of the additional load resistor 233 to thepotential load bus 207 will cause the voltage on the potential load bus207 to decrease. If the voltage on the potential load bus 207 remainsabove the threshold voltage level of 1 Volt, the additional load unitwill be allowed to turn on because the total power output capacity ofthe power supply units 205-0, 205-1, 205-2 will be sufficient. However,if the voltage on the potential load bus 207 falls below the thresholdvoltage level of 1 Volt when the additional load unit is connected, theadditional load unit will not be allowed to turn on because the totalpower output capacity of the power supply units 205-0, 205-1, 205-2 willnot be sufficient.

Once the additional load unit is allowed to turn on, its actual loadresistor 239 will be connected between the actual load bus 211 and thereference ground potential. Then, the voltage on the actual load bus 211will again be the same as the voltage on the potential load bus 207.And, the voltage on the actual load bus 211 will reflect the balancebetween the actual power consumption of the operating load units and thetotal power output capacity of the operating power supply units.

It should be appreciated that the actual load bus 211 providesinformation about the health of the power system 200/200A to the loadunits 203. For instance, in the example power system 300, a voltagedecrease on the actual load bus 211 below the threshold voltage level of1 Volt signals a reduction in total power output capacity of the powersupply units 205 below the total power requirement of the operating loadunits 203, and thereby signals an imminent loss of power event to theload units 203. The load units 203 may then take action to prevent datacorruption and/or may take action to change to a lower operating powerstate in an attempt to prevent power overload of the power supply units205 that remain operational.

In some embodiments, load units 203 may have an ability to operate atdifferent power levels by changing their operating power frequency or byactivating or deactivating load unit 203 parts. In this type ofembodiment, an initial resistance placed on the potential load bus 207for a given load unit 203 may represent the minimum operating powerrequirement of the given load unit 203. Then, in order to test whetherthe power available on the main power bus is adequate to supportincreasing the given load unit 203 to a higher operating power,additional and/or greater resistances representing the increased powerconsumption of the given load unit 203 can be connected between thepotential load bus 207 and the reference ground potential. If thevoltage on the potential load bus 207 remains above the thresholdvoltage level, e.g., 1 V for the example power system 300, the givenload unit 203 is allowed to increase to the higher operating power.However, if the voltage on the potential load bus 207 falls below thethreshold voltage level, the given load unit 203 is not allowed toincrease to the higher operating power. Once the given load unit 203 hasbeen increased to the higher, operating power, a correspondingadditional and/or greater resistance is connected between the actualload bus 211 and the reference ground potential such that the potentialload bus 207 and the actual load bus 211 have an equivalent electricalconnectivity and corresponding equivalent voltage level.

Some computing systems may need to have redundant power capability inorder to achieve sufficient availability in the event of an input powerfailure or power supply unit 205 failure. This redundant powercapability may be referred to as N+N or N+1 power redundancy. The powersystem 200/200A can provide this redundant power capability bypreloading the potential load bus 207 with a resistance that correspondsto the additional power supply capacity needed to provide the requiredredundant power capability. For example, in FIGS. 2A-3, the potentialload bus 207 is preloaded by the resistor 233X, where the resistance ofthe resistor 233X that corresponds to the additional power supplycapacity needed to provide the required redundant power capability. Inthe example power system 300 of FIG. 3, the 1K preload resistor requiresan additional 1 kW of redundant power to be present before the loadunits 203 are allowed to power on. The addition of the 1K preload on thebus requires that the power sources supply an additional 1 mA of currentto raise the voltage on bus 207 to 1 Volt. The additional 1 mA ofcurrent is equivalent to 1 kW of power source capacity.

In one embodiment, the power system 200/200A will delay the initialsupply of power to the main power bus from the power supply units 205until the total power supply capacity exceeds the total power requiredby the connected load units 203 plus the redundant power capabilityrepresented by the preload resistor 233X. And, if the voltage on thepotential load bus 207 is greater than the threshold voltage level, thetotal power supply capacity of the computing system is sufficient toprovide the required redundant power capability. If the voltage on thepotential load bus 207 is not greater than the threshold voltage level,the total power supply capacity of the computing system is notsufficient to provide the required redundant power capability, and theload units 203 will not be allowed to turn on.

FIG. 4 shows an implementation of the load unit 203-2 of the example ofFIG. 3 in power system 200A of FIG. 2B, in accordance with oneembodiment of the present invention. In the power system 200A, the loadunits 203 can include their own intelligent control circuit. Forexample, in FIG. 4, the load unit 203-2 includes an intelligent controlcircuit 401. The intelligent control circuit 401 may be found in loadunits defined for processing, storage, and/or network switching, amongothers. The intelligent control circuit 401 can activated at a low inputpower level in conjunction with issuing a request for permission topower on its load unit 203-2 by operating the controllable connectiondevice 245-2 to connect the load resistor 233-3 between the potentialload bus 207 and the reference ground potential. In this embodiment, thepower supply units 205 can begin operating and providing output power tothe system main power bus 405 as soon as the power supply units 205receive their input power. Then, as the load units 203 ask forpermission to power up through connection of their load resistor 233between the potential load bus 207 and reference ground potential, thevoltage level on the potential load bus 207 will be a function in partof how much power is being supplied to the system main power bus 405 bythe operating power supply units 205. If sufficient power is availableon the system main power bus 405 based on the voltage present on thepotential load bus 207, the load unit 203 will be allowed to power upits main load 403.

It should be understood that the load resistances 233, 239, 233X, 233-0,233-1, 233-2, 239-0, 239-1, 239-2 described in the embodiments hereincan be electrical resistors or essentially any other type of currentsink. For example, any one or more of the load resistances 233, 239,233X, 233-0, 233-1, 233-2, 239-0, 239-1, 239-2 can be replaced bycircuitry defined to sink the same current to the reference ground in amanner independent of the voltage level on the bus (207, 211) to whichthe load resistance is connected.

It may be necessary to manage multiple load units 203 trying to ask forpermission to power up their main loads 403 at the same time in order toavoid collisions on the system main power bus 405. For example, in oneembodiment, collisions on the system main power bus 405 can be avoidedby assigning each load unit 203 a delay time for requesting power upbased on the load unit's 203 location in the computing system rack,since load units 203 would normally know where they are located tofacilitate servicing. Also, to manage retry requests for power up, eachload unit 203 can be assigned a retry waiting period after which theload unit 203 can retry for permission to power up its main load 403.Thus, if the load unit 203 had failed to receive permission to power upits main load 403 on a previous attempt, the load unit 203 can retry forpermission to power up after it assigned retry waiting period haselapsed. One feature of the power system 200A is that load units 203 canbegin reporting their status and the status of the power system 200A assoon as input power is available to one of the power supply units 205.Then, if additional power supply units 205 do not receive their inputpower to allow all load units 203 to be made operational, the situationcan be reported to service personnel for correction.

Based on the foregoing, it should be appreciated that the power system200/200A provides the following features, among others, without the costand complexity associated with a microprocessor-based power controllermodule:

-   -   Initial start or restart of the computing system is accomplished        without danger of power supply units 205 overload.    -   New load units 203 added to an operating computing system will        be prohibited from turning on if they have the potential of        overloading the power supply units 205 or, as an option, causing        the computing system to have less than the desired reserve power        capacity.

Additionally, it should be appreciated that the power system 200/200Adisclosed herein provides a simple way to quickly inform the load units203 of a decrease in power supply units 205 capability that might resultin power output failure. In conventional power systems, it may bedifficult to quickly determine if the loss of a single power supply unitwill cause the whole power system to overload, i.e., cause a powerfault. However, in the power system 200/200A of the present invention,false power fault alarms can be prevented by using the voltage level onthe actual load bus 211 as an indication as to whether or not theremaining power output capacity of the power supply unit(s) 205 issufficient to satisfy the operating load unit(s) 203 power requirements,and thereby avoid a power fault.

FIG. 5A shows a flowchart of a method for operating a power system, inaccordance with one embodiment of the present invention. The methodincludes an operation 501 for applying a separate electrical current toa potential load bus for each of a number of operating power supplyunits. Each separate electrical current applied to the potential loadbus is scaled in magnitude relative to a power supply capability of agiven power supply unit to which the separate electrical currentcorresponds. The method includes an operation 503 for connecting aseparate resistor between the potential load bus and a reference groundpotential for each of a number of load units that are to receive powerfrom the number of operating power supply units. Each separate resistorconnected to the potential load bus has an electrical resistance scaledin magnitude relative to a power consumption of a given load unit towhich the separate resistor corresponds. The method includes anoperation 505 for comparing a voltage level on the potential load bus toa threshold voltage level to determine whether or not a sufficientsupply of power is available from the number of operating power supplyunits for operation of the number of load units.

The method can also include an operation for setting the thresholdvoltage level based on each separate electrical current applied to thepotential load bus and each separate resistor connected to the potentialload bus such that when the supply of power available from the number ofoperating power supply units exceeds a total power consumption of thenumber of load units, a voltage level on the potential load bus exceedsthe threshold voltage level. And, upon determining that the voltagelevel on the potential load bus exceeds the threshold voltage level, themethod can include an operation for providing power to the number ofload units.

In one embodiment, operation 503 is performed such that the separateresistor is connected between the potential load bus and the referenceground potential for the number of load units in a sequential manner. Inthis embodiment, upon determining that the voltage level on thepotential load bus exceeds the threshold voltage level for connection ofa given separate resistor to the potential load bus, the method includesproviding power to a load unit corresponding to the given separateresistor. In another embodiment, the method includes releasing powerfrom the number of operating power supply units to the number of loadunits upon verifying that the voltage on the potential load bus exceedsthe threshold voltage level after connecting the separate resistorbetween the potential load bus and the reference ground potential foreach of the number of load units.

FIG. 5B shows a flowchart of a method for operating a power system, inaccordance with one embodiment of the present invention. In oneembodiment, the method of FIG. 5B is performed in conjunction with themethod of FIG. 5A. In another embodiment, the method of FIG. 5B isperformed separate from the method of FIG. 5A. The method includes anoperation 507 for applying a separate electrical current to an activeload bus for each of a number of operating power supply units. Eachseparate electrical current applied to the active load bus is scaled inmagnitude relative to a power supply capability of a given power supplyunit to which the separate electrical current corresponds. The methodalso includes an operation 509 for connecting a separate resistorbetween the active load bus and the reference ground potential for eachof the number of load units that are actively receiving power from thenumber of operating power supply units. Each separate resistor connectedto the active load bus has an electrical resistance scaled in magnituderelative to a power consumption of a given load unit to which theseparate resistor corresponds. The method also includes an operation 511for transmitting a loss of power signal to one or more of the number ofload units when the voltage level on the active load bus decreases belowthe threshold voltage level. The method can also include receiving theloss of power signal at one or more of the number of load units, and inresponse to receiving the loss of power signal, operating the one ormore of the number of load units to prepare for an imminent loss ofpower event.

FIG. 6A shows a flowchart of a method for configuring a power system, inaccordance with one embodiment of the present invention. The methodincludes an operation 601 for installing a number of power supply units.The method also includes an operation 603 for installing a number ofload units. The method also includes an operation 605 for connecting thenumber of load units to receive power from the number of power supplyunits. The method also includes an operation 607 for connecting aseparate first electric current source to supply electrical current to apotential load bus for each of the number of power supply units. Eachfirst electrical current source is defined to supply an amount ofelectrical current based on a power output rating of a given one of thenumber of power supply units to which it corresponds. The method alsoincludes an operation 609 for connecting a separate first resistor tothe potential load bus for each of the number of load units. Each firstresistor is defined to provide an amount of electrical resistance basedon a power consumption of a given one of the number of load units towhich it corresponds. The method also includes an operation 611 forconnecting a separate first voltage comparator device to the potentialload bus for each of the number of load units. Each first voltagecomparator device has a first input connected to the potential load busand a second input connected to a reference voltage supply to be set ata threshold voltage level and an output connected to a power controlcircuit of a given one of the number of load units to which itcorresponds.

FIG. 6B shows a flowchart of a method for configuring a power system, inaccordance with one embodiment of the present invention. In oneembodiment, the method of FIG. 6B is performed in conjunction with themethod of FIG. 6A. In another embodiment, the method of FIG. 6B isperformed separate from the method of FIG. 6A.

The method includes an operation 613 for connecting a separate secondelectric current source to supply electrical current to an active loadbus for each of the number of power supply units. Each second electriccurrent source is defined to supply an amount of electrical currentbased on a power output rating of a given one of the number of powersupply units to which it corresponds. The method also includes anoperation 615 for connecting a separate second resistor to the activeload bus for each of the number of load units that is actively receivingpower from the number of power supply units. Each second resistor isdefined to provide an amount of electrical resistance based on a powerconsumption of a given one of the number of load units to which itcorresponds. The method further includes an operation 617 for connectinga separate second voltage comparator device to the active load bus foreach of the number of load units that is actively receiving power fromthe number of power supply units. Each voltage comparator device has afirst input connected to the active load bus and a second inputconnected to a reference voltage supply to be set at the thresholdvoltage level and an output connected to transmit of a loss of powersignal to each of the number of load units when a voltage level on theactive load bus decreases below the threshold voltage level.

With the above embodiments in mind, it should be understood that thepresent invention may employ various computer-implemented operationsinvolving data stored in computer systems. These operations are thoserequiring physical manipulation of physical quantities. Usually, thoughnot necessarily, these quantities take the form of electrical ormagnetic signals capable of being stored, transferred, combined,compared, and otherwise manipulated. Further, the manipulationsperformed are often referred to in terms, such as producing,identifying, determining, or comparing.

Any of the operations described herein that form part of the inventionare useful machine operations. The invention also relates to a device oran apparatus for performing these operations. The apparatus may bespecially constructed for the required purposes, or it may be ageneral-purpose computer selectively activated or configured by acomputer program stored in the computer. In particular, variousgeneral-purpose machines may be used with computer programs written inaccordance with the teachings herein, or it may be more convenient toconstruct a more specialized apparatus to perform the requiredoperations.

Parts of the invention can also be embodied as computer readable code ona computer readable medium. The computer readable medium is anynon-transitory data storage device that can store data which can bethereafter be read by a computer system. Examples of the computerreadable medium include hard drives, network attached storage (NAS),read-only memory, random-access memory, CD-ROMs, CD-Rs, CD-RWs, DVDs,magnetic tapes, and other optical and non-optical data storage devices.The computer readable medium can also be distributed over a networkcoupled computer systems so that the computer readable code is storedand executed in a distributed fashion.

While this invention has been described in terms of several embodiments,it will be appreciated that those skilled in the art upon reading thepreceding specifications and studying the drawings will realize variousalterations, additions, permutations and equivalents thereof. It istherefore intended that the present invention includes all suchalterations, additions, permutations, and equivalents as fall within thetrue spirit and scope of the invention.

What is claimed is:
 1. A power system, comprising: a number of powersupply units; a number of load units connected to receive power from henumber of power supply units; a potential load bus connected to have avoltage level representative of both a total potential power requirementof the number of load units and a total potential power supplycapability of the number of power supply units; a first control circuitconnected to the potential load bus and defined to monitor the voltagelevel on the potential load bus and enable operation of one or more ofthe number of load units when the voltage level on the potential loadbus indicates that a sufficient supply of power is available from thenumber of power supply units for operation of the one or more of thenumber of load units; an actual load bus connected to have a voltagelevel representative of both an actual total power consumption of thenumber of load units and an actual total power supply available from ofthe number of power supply units; and a second control circuit connectedto the actual load bus and defined to monitor the voltage level on theactual load bus and based on the monitored voltage level on the actualload bus signal an impending loss of the sufficient supply of power fromthe number of power supply units for operation of the one or more of thenumber of load units.
 2. A power system as recited in claim 1, whereinthe first control circuit is defined to compare the voltage level of thepotential load bus to a threshold voltage level to determine whether ornot each of the number of load units is to be enabled for operation. 3.A power system as recited in claim 2, wherein the first control circuitis defined to enable the number of load units for operation on anindividual load unit basis when the voltage level of the potential loadbus is greater than the threshold voltage level.
 4. A power system asrecited in claim 3, wherein the first control circuit includes separatevoltage comparator devices respectively connected to the number of loadunits, each of the separate voltage comparator devices having a firstinput connected to the potential load bus and a second input connectedto a reference voltage supply to be set at the threshold voltage leveland an output connected to a power control circuit of the load unit towhich the voltage comparator device is connected.
 5. A power system asrecited in claim 1, wherein the second control circuit is defined tocompare the voltage level of the actual load bus to a threshold voltagelevel to determine whether or not an actual total supply of power fromthe number of power supply units is sufficient to support continuedoperation of the number of load units that are in an operating state. 6.A power system as recited in claim 5, wherein the second control circuitis defined to transmit a power fault warning signal when the voltagelevel of the actual load bus is less than the threshold voltage level.7. A power system as recited in claim 6, wherein the power fault warningsignal is transmitted instantaneously and continuously from the secondcontrol circuit to each of the number of load units when the voltagelevel of the actual load bus is less than the threshold voltage level.8. A power system as recited in claim 6, wherein the second controlcircuit includes separate voltage comparator devices respectivelyconnected to the number of load units, each of the separate voltagecomparator devices having an output connected to a power control circuitof the load unit to which the voltage comparator device is connected,each of the separate voltage comparator devices having a first inputconnected to the actual load bus and a second input connected to areference voltage supply to be set at the threshold voltage level.
 9. Apower system as recited in claim 1, further comprising: a first numberof resistors connected between the potential load bus and a referenceground potential, the first number of resistors respectivelycorresponding to the number of load units, each of the first number ofresistors having an amount of electrical resistance based on a powerconsumption of the load unit to which it corresponds; and a first numberof current sources connected to supply electrical current to thepotential load bus, the first number of current sources respectivelycorresponding to the number of power supply units, each of the firstnumber of current sources defined to supply an amount of electricalcurrent based on a power output rating of the power supply unit to whichit corresponds.
 10. A power system as recited in claim 9, wherein thefirst number of resistors includes at least one resistor that does notcorrespond to one of the number of load units, the at least one resistorhaving an amount of electrical resistance based on a prescribed amountof power supply margin.
 11. A power system as recited in claim 9,further comprising: a second number of resistors connected between theactual load bus and the reference ground potential through acorresponding controllable connection device defined to connect when acorresponding load unit is an operating state, the second number ofresistors respectively corresponding to the number of load units, eachof the second number of resistors having an amount of electricalresistance based on power consumption of the load unit to which itcorresponds, such that for a given one of the number of load units theamount of electrical resistance of each of the corresponding one of thesecond number of resistors and the corresponding one of the first numberof resistors is substantially equal; and a second number of currentsources connected to supply electrical current to the actual load bus,the second number of current sources respectively corresponding to thenumber of power supply units, each of the second number of currentsources defined to supply an amount of electrical current based on apower output rating of the power supply unit to which it corresponds,such that for a given one of the number of power supply units the amountof electrical current to be supplied by each of the corresponding one ofthe second number of current sources and the corresponding one of thefirst number of current sources is substantially equal.
 12. A powersystem as recited in claim 11, wherein each of the number of powersupply units is defined to control activation of its corresponding oneof the first number of current sources and its corresponding one of thesecond number of current sources.
 13. A power system as recited in claim1, further comprising: a first number of resistors respectivelycorresponding to the number of load units, each of the first number ofresistors having an amount of electrical resistance based on a powerconsumption of the load unit to which it corresponds; a number ofcontrollable connection devices respectively connected to the firstnumber of resistors to provide individual control of an electricalconnection between the first number of resistors and a reference groundpotential, such that a given one of the first number of resistors isconnected to the reference ground potential when the load unitcorresponding to the given one of the first number of resistors issues arequest to receive power; and a first number of current sourcesconnected to supply electrical current to the potential load bus, thefirst number of current sources respectively corresponding to the numberof power supply units, each of the first number of current sourcesdefined to supply an amount of electrical current based on a poweroutput rating of the power supply unit to which it corresponds.
 14. Apower system as recited in claim 1, further comprising: a third controlcircuit defined to disable output of power from the number of powersupply units to the number of load units until an actual total availablesupply of power from the number of power supply units is sufficient tosupport operation of the number of load units, and wherein the thirdcontrol circuit is defined to enable output of power from the number ofpower supply units to the number of load units when the actual totalavailable supply of power from the number of power supply units issufficient to support operation of the number of load units.
 15. A powersystem as recited in claim 14, wherein the third control circuit isdefined to compare the voltage level of the potential load bus to athreshold voltage level to determine whether or not output of power fromthe number of power supply units is to be enabled or disabled.
 16. Apower system as recited in claim 15, wherein the third control circuitis defined to enable output of power from the number of power supplyunits to the number of load units when the voltage level of thepotential load bus is greater than the threshold voltage level, andwherein the third control circuit is defined to disable output of powerfrom the number of power supply units to the number of load units whenthe voltage level of the potential load bus is less than the thresholdvoltage level.
 17. A power system as recited in claim 16, wherein thethird control circuit includes separate voltage comparator devicesrespectively connected to the number of power supply units, each of theseparate voltage comparator devices having a first input connected tothe potential load bus and a second input connected to a referencevoltage supply to be set at the threshold voltage level, each of theseparate voltage comparator devices having an output connected to apower output control of the power supply unit to which the voltagecomparator device is connected.
 18. A method for operating a powersystem, comprising: applying a separate electrical current to apotential load bus for each of a number of operating power supply units,wherein each separate electrical current applied to the potential loadbus is scaled in magnitude relative to a power supply capability of agiven power supply unit to which the separate electrical currentcorresponds; connecting a separate resistor between the potential loadbus and a reference ground potential for each of a number of load unitsthat are to receive power from the number of operating power supplyunits, wherein each separate resistor connected to the potential loadbus has an electrical resistance scaled in magnitude relative to a powerconsumption of a given load unit to which the separate resistorcorresponds; and comparing a voltage level on the potential load bus toa threshold voltage level to determine whether or not a sufficientsupply of power is available from the number of operating power supplyunits for operation of the number of load units.
 19. A method foroperating a power system as recited in claim 18, further comprising:setting the threshold voltage level based on each separate electricalcurrent applied to the potential load bus and each separate resistorconnected to the potential load bus such that when the supply of poweravailable from the number of operating power supply units exceeds atotal power consumption of the number of load units, a voltage level onthe potential load bus exceeds the threshold voltage level.
 20. A methodfor operating a power system as recited in claim 19, further comprising:upon determining that the voltage level on the potential load busexceeds the threshold voltage level, providing power to the number ofload units.
 21. A method for operating a power system as recited inclaim 20, wherein the separate resistor is connected between thepotential load bus and the reference ground potential for the number ofload units in a sequential manner, and wherein upon determining that thevoltage level on the potential load bus exceeds the threshold voltagelevel for connection of a given separate resistor to the potential loadbus, providing power to a load unit corresponding to the given separateresistor.
 22. A method for operating a power system as recited in claim19, further comprising: releasing power from the number of operatingpower supply units to the number of load units upon verifying that thevoltage on the potential load bus exceeds the threshold voltage levelafter connecting the separate resistor between the potential load busand the reference ground potential for each of the number of load units.23. A method for operating a power system as recited in claim 19,further comprising: applying a separate electrical current to an activeload bus for each of the number of operating power supply units, whereineach separate electrical current applied to the active load bus isscaled in magnitude relative to a power supply capability of a givenpower supply unit to which the separate electrical current corresponds;connecting a separate resistor between the active load bus and thereference ground potential for each of the number of load units that areactively receiving power from the number of operating power supplyunits, wherein each separate resistor connected to the active load bushas an electrical resistance scaled in magnitude relative to a powerconsumption of a given load unit to which the separate resistorcorresponds; and transmitting a loss of power signal to one or more ofthe number of load units when the voltage level on the active load busdecreases below the threshold voltage level.
 24. A method for operatinga power system as recited in claim 23, further comprising: receiving theloss of power signal at one or more of the number of load units, and inresponse to receiving the loss of power signal, operating the one ormore of the number of load units to prepare for an imminent loss ofpower event.
 25. A method for configuring a power system, comprising:installing a number of power supply units; installing a number of loadunits; connecting the number of load units to receive power from thenumber of power supply units; connecting a separate first electriccurrent source to supply electrical current to a potential load bus foreach of the number of power supply units, wherein each first electricalcurrent source is defined to supply an amount of electrical currentbased on a power output rating of a given one of the number of powersupply units to which it corresponds; connecting a separate firstresistor to the potential load bus for each of the number of load units,wherein each first resistor is defined to provide an amount ofelectrical resistance based on a power consumption of a given one of thenumber of load units to which it corresponds; and connecting a separatefirst voltage comparator device to the potential load bus for each ofthe number of load units, wherein each first voltage comparator devicehas a first input connected to the potential load bus and a second inputconnected to a reference voltage supply to be set at a threshold voltagelevel and an output connected to a power control circuit of a given oneof the number of load units to which it corresponds.
 26. A method forconfiguring a power system as recited in claim 25, further comprising:connecting a separate second electric current source to supplyelectrical current to an active load bus for each of the number of powersupply units, wherein each second electric current source is defined tosupply an amount of electrical current based on a power output rating ofa given one of the number of power supply units to which it corresponds;connecting a separate second resistor to the active load bus for each ofthe number of load units that is actively receiving power from thenumber of power supply units, wherein each second resistor is defined toprovide an amount of electrical resistance based on a power consumptionof a given one of the number of load units to which it corresponds; andconnecting a separate second voltage comparator device to the activeload bus for each of the number of load units that is actively receivingpower from the number of power supply units, wherein each voltagecomparator device has a first input connected to the active load bus anda second input connected to a reference voltage supply to be set at thethreshold voltage level and an output connected to transmit of a loss ofpower signal to each of the number of load units when a voltage level onthe active load bus decreases below the threshold voltage level.